Modern electronic equipment such as televisions, telephones, radios and computers are generally constructed of solid state devices. Solid state devices are preferred in electronic equipment because they are extremely small and relatively inexpensive. Additionally, solid state devices are very reliable because they have no moving parts, but are based on the movement of charge carriers.
Solid state devices may be transistors, capacitors, resistors, and other semiconductor devices. Typically, such devices are fabricated on a substrate and interconnected to form memory arrays, logic structures, timers and other integrated circuits. One type of memory array is a dynamic random access memory (DRAM) in which memory cells retain information only temporarily and are refreshed at periodic intervals. Despite this limitation, DRAMs are widely used because they provide low cost per bit of memory, high device density, and feasibility of use.
In a DRAM, each memory cell typically includes an access transistor coupled to a storage capacitor. In order to fabricate high density DRAMs, the storage capacitors must take up less planar area in the memory cells. As storage capacitors are scaled down in dimensions, a sufficiently high storage capacity must be maintained. Efforts to maintain storage capacity have concentrated on building three-dimensional capacitor structures that increase the capacitor surface area. The increased surface area provides for increased storage capacity. Three-dimensional capacitor structures include trench capacitors and stacked capacitors.
For stacked capacitors, the storage node generally extends significantly above the surface of an underlying substrate in order to provide a large surface area and thus sufficient storage capacity. This leads to topological problems in the formation of subsequent layers in the DRAM. Such topological problems are reduced by the use of crown-type stacked capacitors that increase surface area of the storage node while minimizing height. Crown-type capacitors, however, have a high process complexity which leads to high fabrication cost and low yield.